Jon Stewart regrets buying that yellow Livestrong bracelet now that Lance Armstrong has admitted to using performance-enhancing drugs.

The disgraced cyclist told Oprah Winfrey in a two-part interview set to air on Thursday and Friday that he cheated by using the drugs throughout his long career.

"I believed in you, Lance Armstrong!" Stewart said on his show Tuesday night. "I shelled out a dollar for a rubber bracelet that I have somewhere in my house. For you!"

Stewart said that given his winning seven Tour de France titles after having testicular cancer, it's been obvious all along that Armstrong had been doping: "Any idiot with half a brain show have been able to see that Armstrong was lying" he said -- before running a clip of a 2006 interview he did with the cyclist.

In the interview, he asked the biker: "They've been testing you like crazy ... don't the results speak for themselves at some point?"

"Nailed it again," he said, laughing at himself. "You know what, for as good at interviewing as I am, I would not be surprised if Armstrong was also banging David Petraeus."

Earlier on Wednesday, Livestrong, the cancer charity for which Armstrong served as a poster boy, issued a terse statement about his upcoming interview.

"We expect Lance to be completely truthful and forthcoming in his interview and with all of us in the cancer community," it said. "We expect we will have more to say at that time."